A guy on DeviantArt made some high-res textless versions of the posters.
https://phetvanburton.deviantart.com/art/A-New-Hope-Hi-Res-Textless-Poster-380226123
That version isn’t very good quality, you’d be better off using a lower resolution image and then enhancing it using waifu2x-caffe. Here’s an example:
Original:
Enhanced:
Will work a lot better of course if you feed it a better image to begin with.